Refinements in Darwin’s theory of the origin of a moral sense create a framework equipped to organize and integrate contemporary theory and research on morality. Morality originated in deferential, cooperative, and altruistic ‘‘social instincts,’’ or decision-making strategies, that enabled early humans to maximize their gains from social living and resolve their conflicts of interest in adaptive ways. Moral judgments, moral norms, and conscience originated from strategic interactions among members of groups who experienced confluences and conflicts of interest. Moral argumentation buttressed by moral reasoning is equipped to generate universal and impartial moral standards. Moral beliefs and standards are products of automatic and controlled information-processing and decision making mechanisms. To understand how people make moral decisions, we must understand how early evolved mechanisms in the old brain and recently evolved mechanisms in the new brain are activated and how they interact. Understanding what a sense of morality is for helps us understand what it is.